Hadoop（+HBaseHDFS）与 Mysql（或 Postgres）——要处理和查询的独立结构化数据负载

Java
import Java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class StudentAverageScore {
  
  public static class ScoreMapper extends Mapper<Object, Text, Text, IntWritable>{
    
    private Text name = new Text();
    private IntWritable score = new IntWritable();
    
    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
      String[] fields = value.toString().split(",");
      name.set(fields[0]);
      score.set(Integer.parseInt(fields[2]));
      context.write(name, score);
    }
  }
  
  public static class AverageReducer extends Reducer<Text, IntWritable, Text, FloatWritable>{
    
    private FloatWritable average = new FloatWritable();
    
    public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
      int sum = 0;
      int count = 0;
      for (IntWritable value : values) {
        sum += value.get();
        count++;
      }
      float avg = (float) sum / count;
      average.set(avg);
      context.write(key, average);
    }
  }
  
  public static void mAIn(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "Student Average Score");
    job.setJarByClass(StudentAverageScore.class);
    job.setMapperClass(ScoreMapper.class);
    job.setReducerClass(AverageReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.wAItForCompletion(true) ? 0 : 1);
  }
}